In the conventional art, in a case in which such as a Web server is provided at a host to which a dynamic global IP address is assigned, in order to access the Web server by using a domain name, a DDNS (dynamic DNS) service is provided in which the Web server is accessed by using a domain name obtained by adding a sub domain name to a domain name that is not originally assigned to the Web server (see Non-Patent Document 1 below). In order to use such a DDNS service, a router provides a function (DDNS client function) which notifies the latest global IP address to a DDNS server when the above-described dynamic global IP address is updated.
By using the above-described DDNS service, for example, it is possible to set up or launch a Web server in one business establishment and to use the Web server for opening a homepage dedicated to clients, customers and company workers.
Non-Patent Document 1: “IT words dictionary e-Words” [online], [searched in Jan. 23, 2006], Internet address <http://e-wordsjp/w/DDNS.html>, by Incept Inc.
However, in a case in which the business establishment becomes larger, for example, in a case in which networks of multiple sites are connected to each other by using a VPN (Virtual Private Network), it is necessary to obtain a self-supporting (not rented) DDNS server. On the other hand, it is necessary to launch the DDNS server by using a host which has a fixed global address. Therefore, in order to obtain the self-supporting (not rented) DDNS server, it is necessary to obtain the fixed global address for the host. However, there is a problem in that it is costly to obtain and maintaining the fixed IP address.